1. Field of the Invention
The present invention relates to a system on chip (SOC) processor, and more particularly, to an SOC processor for a multimedia device.
2. Description of the Related Art
Recently, as multimedia services diversify, various multimedia devices such as mobile phones, PDAs, digital TVs, and DVD players (DVDPs) have been introduced, and the concerns about a processor for a multimedia device have increased.
The processor for a particular multimedia device has various functions, such as image processing, controlling an LCD (liquid-crystal display) or CRT (cathode-ray tube), and controlling hardware and peripheral devices for a video CODEC (coder-decoder). Furthermore, the processor for the multimedia device has been developed as a form of an SOC processor, as there is a need for reducing the cost and the size of the SOC processor.
An SOC processor means an IC (integrated circuit) having a microprocessor, a built-in memory, a plurality of peripheral device controllers, and an external bus interface located on a single chip. Due to the development of the SOC processor, the size of the system can be reduced, the time for system testing is shortened, the reliability of the system is improved, and the product can be launched in the market faster than before.
The SOC processor for the multimedia device is one that includes circuits for performing various functions required by a multimedia device in a single chip. The SOC processor for the multimedia device has been developed from a structure having a circuit of one function such as a DCT (discrete cosine transform) or an ME (motion estimator) to a structure having an SRAM (Static RAM) or a boot ROM (read only memory). Moreover, the SOC processor for the multimedia device has been developed for a chip having a built-in SDRAM (Synchronous DRAM) with vast capacity, and more functions are required due to subsequent technical developments.
However, in the process of designing the SOC processor for the multimedia device, the method of mainly using the microprocessor made by the existing semiconductor manufacturers and adding circuits for required functions can be considered rather than the method of designing an entire processor. In other words, a RISC (reduced instruction set computer) microprocessor (ARM) or a CISC (complex instruction set computer) CPU of x86 (INTEL) or 68k (MOTOROLA) can be used as a main controller in the SOC processor.
Generally, a regulation provided by a semiconductor manufacturer that developed a microprocessor is used as a regulation of a system bus that is used as a common communication path by being connected with the main elements in the system such as a microprocessor, a memory, and an input/output device. A developer can reduce the burden of the design in relation to the external interface and shorten the period of developing the SOC processor by designing the SOC based on the decided regulation.
Yet, in the process of adding various functions for processing on the multimedia device, there is bound to be a difference in the speed of a clock and the processing speed used in the circuits for performing each function. Therefore, when the circuits use a signal common system bus, the operation of the entire system is set with the processing time of a circuit having the slowest processing time or the stand-by status of the circuit having a fast processing time is extended, thus the efficiency of the entire system deteriorates.
Accordingly, for effective design to overcome the difference of the processing time of the circuits, it is preferable that groups of circuits having similar processing time are formed, and that each group uses a separate system bus.
Furthermore, when an unexpected case is encountered, there should be a new system bus appropriate to the new case. In that case, a device for interfacing between the system bus of the existing semiconductor manufacturer and a new designed system bus is required.